Introduce EARLYCON support in hvc_xen, useful for early debugging on arm
and arm64, where xen early_printk is not available.
It is different from xenboot_write_console on x86 in two ways:
- it does not return if !xen_pv_domain(), not only because ARM guests
are xen_hvm_domain(), but also because we want to capture all the
early boot messages, before xen support is discovered
- it does not try to print to the domU console at all, because xen
support will only be discovered at a later point
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
16e506efc0